You can't have SQ in an OW rtw (without buying a separate unrelated ticket on SQ) but I suppose you know that and were just giving an example.

If you decide to fly A class you'll quickly learn that about 95% of what people call "jet lag" after the end of a 12 hour trip in coach is fatigue due to the punishment you've had to endure. 12 hours in first class is a lot like putting in a long day at the office. Your brain will certainly be a bit confused about when to be sleepy, but if in ordinary life you can survive a late night without too much trouble, that's probably how you'll feel at your destination. Our experience has been that east-bound vs west isn't worth planning around.

The most important thing for maximizing rtw pleasure is maximizing the time you spend doing it - 12 months would be way cool, three months worthy. We usually can only eke out 5 or 6 weeks, very much on the low side of good.

You've noticed that if you live in NA and start in Europe or Asia, when you get to NA the first time you'll be "home" and have up to 8 segments to spend, valid from Alaska to Central America, California to the Caribbean. Thus you can have a European vacation, a North American vacation, and an Asian vacation, without necessarily busting one year's vacation budget.

I hold that getting travel advice from anonymous strangers is worse than going on a blind data arranged by randomly picking a name from the phone book. On the date, you can at least go home early. But, just in case any of this appeals to you:
Kruger National Park near Johannesburg is a world-class game-viewing experience, worth a week;
Santorini, especially from Firostefano (sp?), is romantic beyond words;
the train ride between Montreal and Quebec City just before Christmas has a good chance of being beautiful; stay at the Frontenac when you get there;
while we're in Canada, a few days at Chateau Lake Louise, preferably well before tourist season, can be a treat;
the train between Bombay and Goa can be "an experience";
Dusit Santiburi on Koh Samui will spoil you nicely;
Kathmandu, not a OW destination at present, is other-worldly; fly up to Lukla and walk a bit, too;